This invention relates to heart pacing leads of the type adapted for transvenous, endocardial implantation. Such leads are in widespread use, and normally have an exposed, distal tip electrode which is positioned against the inside surface of the heart wall. The elongated, flexible lead comprises an electrical conductor encased within an insulating sheath, and a proximal, connector end for placing the electrode in electrical connection with a pacemaker power source.
Experience has demonstrated that it is important to provide such leads with some type of fixation device for holding the tip electrode in good contact with the heart wall. Such positioning of the electrode is necessary for achieving and maintaining the desired pulse pacing of the heart. Movement or migration of the lead, with attendant dislodgement of the distal electrode, can result in disruption of pacing and/or sensing.
Various fixation mechanisms have been used on pacing leads of the aforesaid type. These include so-called active fixation devices which incorporate some means for positively securing the electrode to the endocardial surface by grasping or direct, penetrating action. Such attachment mechanisms include prongs and pincers which project forwardly from the lead distal end. U.S. Pat. No. 3,754,555 issued to Schmitt on Aug. 28, 1973 discloses leads of this type. Several exampls of leads with active fixation means are shown by E. H. Meese et al in "Initial Clinical Experience with the Ventricular Tined Lead," Proceedings of the VIth World Symposium on Cardiac Pacing. Montreal, Canada, Chapter 31-6, 1979.
The Meese et al article also discloses examples of so-called passive fixation leads, which have tines or other forms of projections such as cones with flanges to catch in the trabeculae of the heart. U.S. Pat. No. 4,030,508 issued to Thalen on June 21, 1977 discloses a conical tipped lead of the previously known type which incorporates a cone having a base flange at its proximal end. The solid cone is not collapsible and is thus made small enough to fit through the smallest size vein for transvenous introduction into the heart. The small diameter of the flange limits its anchoring ability, as is pointed out in U.S. Pat. No. 4,301,815 issued to Carl Doring on Jan. 23, 1980. That patent is directed to a so-called trailing tined lead having tines which project rearwardly from a truncated, conical tip.
Tined leads of the type having tines made from flexible, pliant material, such as silicone rubber, which extend rearwardly at an acute angle from the lead body and can yield and flex upon contact with the walls of veins during transvenous introduction, are disclosed in U.S. Pat. Nos. 3,902,501 and 4,033,357 issued to Citron et al and Helland et al, respectively. Rasor et al also disclose a tined lead in FIG. 12 of U.S. Pat. No. 3,835,864.
Tined leads suffer from the disadvantage that the tines present minimal surface area for entanglement with the trabeculae of the heart. The tines also have been known to catch in the tricuspid valve of the heart during introduction through the heart into the right ventricle.
With this background in mind, a pacemaker lead having an improved fixation mechanism for positive anchoring in the heart has been developed.